The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The state-of-the-art compression standard H.264/AVC enhances coding performance based on predictions using high correlations between neighboring pixels in intra coding.
The intra prediction by H.264/AVC provides a total of nine prediction modes for a block of 4×4 sized unit as illustrated in FIG. 1A, and a total of four prediction modes for a block of 16×16 sized unit as illustrated in FIG. 1B.
Meanwhile, H.264/AVC provides a total of nine intra prediction modes for a block of 8×8 sized unit as with the block of 4×4 sized unit, and first applies a filter for removing high frequency components to reference pixels of the neighboring blocks to be used for the prediction to smooth the reference pixels prior to performing the prediction [Document 1]. In the filtering process, the neighboring pixels may be changed to have values more suitable for the intra prediction to decrease intra prediction errors for target blocks.
However, the filtering for removing high frequency components of the reference pixels attenuates AC components actually present among original pixels, such that it may be difficult to provide details of block data to be predicted and in some cases, prediction performance or efficiency may be relatively more degraded than the case in which the filtering is not applied.
To solve the shortcoming, an adaptive filtering method was proposed by Fraunhofer Heinrich Hertz Institute (hereinafter, referred to as HHI) in HEVC that is a meeting for establishing a standard of the next-generation moving picture compression encoding/decoding device [Document 2].
The adaptive filtering method proposed by the HHI compares the prediction error occurring when the filtering for removing high frequency components is applied to each block for intra prediction against the prediction error occurring without the same filtering applied and as a comparison results, applies the smaller prediction errors to the actual encoding, thereby reducing the prediction errors.
However, the decoding apparatus requires an additional amount of information for each prediction block unit to perform indexing of whether or not to apply filtering, which may rather cause deteriorated compression efficiency for such images that would show little decrement of prediction errors with the adaptive filtering.
[Document 1]
1. Telecommunication Standardization sector of ITU, ““ITU-T Recommendation H.264, Series H: Audiovisual and Multimedia Systems, Advanced video coding for generic audiovisual services””, ITU-T Recommendation H.264, pp. 132-133, November 2007.
2. Martin Winken, Sebastian Boββe, ““Description of video coding technology proposal by Fraunhofer HHI””, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, CfP response proposal JCTVC-A116, April 2010